As dose calculations, high energy treatment machines, and treatment techniques in radiotherapy become more sophisticated, there is a need at present to develop a practical areal dosimeter of sufficient accuracy and resolution for rapid acquistion of dosimetric data. Film dosimetry is inadequate because of its poor precision while ionization dosimetry is timeconsuming. A novel approach to areal dosimetry using plastic scintillator is proposed here. Plastic scintillator has appealing qualities as a dosimeter because of its waterlike properties. The high radiation intensity available in radiotherapy makes it possible to obtain dosimetric data from a sheet of plastic scintillator using a video camera to view the scintillation light. Our long term objective is to develop a practical dosimeter system capable of making precise areal measurements, based on a plastic scintillator sheet viewed by a video camera whose output is acquired and analyzed by computer. A prototype data acquisition system has been assembled for preliminary studies of external photon and electron been dosimetry. These recent results are encouraging, and demonstrate the feasibility of the approach. As the next step in the development of this system, we propose to (1) design and build a water tank dosimetry system based on a plastic scintillator sheet for external photon and electron beam dosimetric studies; (2) develop the instrument as a quantitative dosimetry system by studying instrument artifacts and the underlying physics; (3) characterize the properties of the dosimetry system in terms of precision of dose measurement, resolution, etc; and (4) use the system for feasibility studies in brachytherapy dosimetery applications.